EFFECT OF NO_3~-, NO_2~- AND Cl~- ON THE CORROSION BEHAVIOUR OF (LEAD-TIN) ALLOY IN ACID MEDIUM

摘要

Corrosion of (lead-tin) alloy (34.5% lead and 65.5% tin) in deaerated solutions of 0.1 M oxalic, tartaric and citric acid solutions in presence and absence of NO_2~-, NO_3~- and Cl~- ions was studied by means of potential-time, corrosion rate and galvanostatic technique within the pH range 2.5 - 6.5 for 0.1 M of the three acids. At pH 4.5, there is a maximum negative potential for oxalic acid and at pH 5.5 for tartaric and citric acid solutions. From pH 2.5 to 4.5 the corrosion mechanism is anodically controlled by reaction of Sn~(++) ion with anion of the tested acids. The potential of the alloy electrode is reduced in the presence of Cl~-, NO_3~- and NO_2~-. This may be due to the attack of the oxide film by the tested anions, then followed by film repair via the insoluble complex species. Corrosion rate and corrosion current I_(corr) of the alloy increase as compared to pure tin results.